Thinking Holistically

Pest Control Chain Reaction
To treat a malaria outbreak in Borneo in the 1950s, the World Health Organization (WHO) sprayed DDT to kill mosquitoes. But the DDT also killed parasitic wasps which were controlling thatch-eating caterpillars. As a result, the thatched roofs of many homes fell down, and the DDT-poisoned insects were eaten by geckoes, which were in turn eaten by cats. The cats perished, which led to the multiplication of rats, and then outbreaks of sylvatic plague and typhus.
To put an end to this destructive chain of events, WHO had to parachute 145,000 live cats into the area to control the rats.